Food businesses have been told to send initial test results on all their products to the FSA by Friday.

"The retailers have committed to conduct more tests and in the interests of public confidence I`ve asked them to publish them on a quarterly basis," Paterson said, adding that there was no evidence yet that the scandal had become a public safety issue.

Paterson said the scandal was either due to "gross incompetence" or an international criminal "conspiracy".

Sources close to the Department for the Environment, Food and Rural Affairs (Defra) and the FSA said it appeared that the contamination of beefburgers, lasagne and other products was the result of fraud that had an "international dimension".

The Metropolitan police had been asked to investigate the scandal and Paterson suggested the scandal was potentially a "worldwide" issue.

Experts within the horse slaughter industry have told the Observer there is evidence that both Polish and Italian mafia gangs are running multimillion-pound scams to substitute horsemeat for beef during food production.

There are claims that vets and other officials working within abattoirs and food production plants are intimidated into signing off meat as beef when it is in fact cheaper alternatives such as pork or horse.

Meanwhile, the FSA was accused of a shambolic handling of the escalating scandal after it emerged that it is failing to stop exports of carcasses that could contain a banned drug harmful to humans.

A sample of 1.6 per cent of the more than 9,000 British horse carcasses exported to European markets showed five contaminated with phenylbutazone, also known as bute, which is banned in the human food chain, The Independent today claimed in a report.

Concerns about the substitution of horsemeat for beef first emerged in mid-January when supermarket chains withdrew several ranges of burgers. Fears of contamination prompted hundreds of European food companies to conduct DNA checks on their products.